There is known a device described in a following patent document 1, as a conventional power steering apparatus.
The power steering apparatus includes a steering mechanism arranged to steer a steered wheel in accordance with an operation of a steering wheel, and an electric motor arranged to provide a steering force to the steering mechanism.
Moreover, the power steering apparatus includes a steering angle sensor arranged to sense a steering angle of the steering wheel. The control and so on of the motor is performed based on the steering angle.
The steering angle sensor includes a first gear which includes a magnetic member, and which is arranged to be rotated in accordance with the rotation of the steering wheel, and a second gear which includes a magnetic member, which is engaged with the first gear to be rotated, and whose a number of teeth is different from that of the first gear.
The steering angle sensor includes two detection elements arranged to sense rotation angles (first and second rotation angles) of the first and second gears from variations of magnetic fields of the magnetic members. The steering angle sensor is arranged to sense the steering angle (absolute steering angle) which is a rotation amount from a neutral position of the steering wheel, based on an angle different of the first and second rotation angles.
By the way, in the conventional power steering apparatus, the gears are easily (carelessly) assembled to the steering angle sensor without consideration of the rotation angles.
In this case, the absolute steering angle outputted from the steering angle sensor may be deviated from the steering angle (actual steering angle) of the steering wheel by a predetermined angle. The steering angle sensor is arranged to calibrate this deviation of the angle so that the absolute steering angle corresponds to the actual steering angle.
However, the absolute steering angle sensed by the above-described method is based on the calibration. Accordingly, for example, in a case where it is not possible to refer to a correction value due to failure (malfunction) of a nonvolatile storage and so on which stores the correction value for the calibration, the absolute steering angle is calculated based on the angle difference of the uncorrected rotation angles. Accordingly, a different between the absolute steering angle and the actual steering angle may be generated.